Dampers (shock absorbers and struts) are used in automobile suspension systems. The telescopic piston rod and seals of a damper must be protected from the elements. Further, the mount assembly, bearing, and damper must be protected from coming in contact with one another during suspension travel.
A jounce bumper is a tubular member that is slipped over the piston rod of the damper. The jounce bumper protects the mount assembly from coming into contact with the striker plate of the damper. The jounce bumper is compressed as a damper bottoms out on a compression or jounce stroke to dissipate jounce energy, thus, protecting the mount assembly.
A bellows (dust shield or sheath) is used to protect the piston rod and seals from the elements. It has a hollow cylindrical body that is slipped over an upper end of the piston rod on the damper. The bellows includes a portion of inner and outer convolutions on the outer surface of the body. Such convolutions provide a spring-like effect by permitting the bellows to be compressed when the damper is in a compression stroke and by causing the bellows to expand to its approximate original length during rebound of the damper.
Prior art products are disadvantageous in that each model of automobile contains a different damper that requires a different bumper/bellows design. As there are well over a 100 different models on the market today, and it is not cost-effective to make 100 separate bumpers and 100 separate bellows to cover each applicable damper.
The most common bellows is an elastic sheath. One end of the sheath is connected to the jounce bumper by way of a metallic strap or interlocking groves, while the other end is open. The connected bumper and bellows is slipped over the piston rod of the damper, where the open end of the sheath allows it to pass over the reservoir tube of the damper during suspension travel.
This two-piece system is disadvantageous in that the open-ended sheath does not prevent the elements from entering the bottom of the unit and damaging the piston rod and seals of the damper. Further, the attachment method for connecting the jounce bumper and dust shield is a mechanical method that uses additional parts (mechanical strap) or interlocking groves to hold the two individual parts together. Time must be taken, and alternate methods must be used to accomplish connecting the two items. Lastly, the multiple part assembly is expensive to manufacture and takes a longer time to produce.
Other systems use a bellows connected to a jounce bumper, through either an interlocking grove or a third part (interlocking ring), on one end, and mechanically attached to the reservoir tube on the other end with a fourth part, i.e., via a tie-strap or clamp.
This system is disadvantageous in that there are three to four separate parts, that require assembly. The connection is also very unstable, for example, a severe drop in the suspension (i.e., driving over a pot-hole) can cause the bumper and bellows to separate, thereby causing the top of the bellows to fall. This in turn causes the exposure of the piston rod and seals to the elements. Further, this multiple part assembly requires the use of a mechanical tie-strap or clamp that may become unattached from the damper, thus causing exposure of the piston rod and seals. There are still two openings on either side of the bellows that allow contamination of the interior. When installing the unit, it is difficult to fit the jounce bumper over the major diameter of the piston rod. Lastly, the multiple part system is more expensive to manufacture and takes a longer time to produce.
In another design, illustrated in U.S. Pat. No. 5,275,389, the jounce bumper uses a collar that "traps" the bellows between the jounce bumper and an upper metal washer. The bellows design in this patent is a combination of a sheath and a bellows. This system is disadvantageous in that the lower end of the bellows that slips over the reservoir tube is open, which exposes the piston rod and seals of the damper to the elements. Further, this multiple part system is more expensive and time-consuming to manufacture.